Linerless labels are becoming increasingly popular because of the environmental and other advantages associated with them. Oftentimes the linerless labels are printed, particularly with thermal printers, such as a Moore Millennium Linerless Label Printer available from Moore Business Forms of Lake Forest, Ill. and the Datamax Prodigy Plus.TM. linerless label printer available from Datamax of Eden Prairie, Minn. Such printers, and most other thermal printers, have a thermal print head which squeezes the label between itself and a drive roller which has a non-stick coating (such as a plasma coating or silicone coating). For example, in the Datamax Prodigy Plus.TM. Printer the print head exerts approximately a 9.5 pound compressive force, which is necessary to insure good print quality and a positive driving force to feed the label through the printer. While this compressive force is necessary for proper operation, even though the drive roller peripheral surface has a non-stick configuration, it is still possible for the adhesive of a label to stick to the drive roller peripheral surface. According to the present invention it has been found that this occurs primarily during a particular sequence of operation of the printer, and when the adhesive is a particularly aggressive adhesive, such as a permanent pressure sensitive adhesive (as opposed to removable or repositional pressure sensitive adhesives).
In typical operation of a Datamax Prodigy Plus.upsilon. printer to print linerless labels, the operator selects and inputs a quantity of labels to run in a batch. The printer recognizes a signal from the software of the computer and receives a first format for setting up the printer, e.g. which is data about the particular labels to be printed including perhaps graphics, text, bar codes, relative positioning, desired label length, etc. The printer then backfeeds the label and parks the leading edge under the print head until a second format is loaded. Once a second format is loaded, the printer advances the leading label of the roll and prints the first label. Depending upon the complexity of the formats the label may be parked under the print head for as long as two to three seconds while formatting. It has been recognized that when a label is parked under the print head without immediately being advanced the label's adhesive starts to attract or grab the non-stick peripheral surface of the drive roller. When the label is finally advanced, the drive roller does not have enough time to release the label and, therefore, the label wraps around the roller or jams the printer. There can be sticking at other times, too, where particularly aggressive pressure sensitive adhesives are provided on the labels.
According to the present invention various methods and apparatus are utilized for solving the problem described above. According to the present invention by modifying the operation of the thermal printer, and/or by directing a substantially uniform stream of gas under pressure to the interface area between the label and the drive roller peripheral surface it is possible, to prevent the labels from wrapping around the roller when it is rotated. A change in printer operation is effected merely by changing the sequence of operation in the firmware of the printer (that is, in the printer computer control chip).
According to one aspect of the present invention a method of operating a printer having a non-stick peripheral surface drive roller, cutter, and print head to print linerless labels in a roll having a printable first face and a second face with pressure sensitive adhesive without the pressure sensitive adhesive sticking to the drive roller, is provided. While the invention is particularly applicable to thermal printers it is not limited to them, but may be used with other linerless label printers. The method comprises the steps of substantially sequentially: (a) Operating the drive roller to advance the roll of linerless labels so that the second face is in contact with the drive roller and so that the leading edge of the linerless labels in the roll is aligned with the cutter, in a first position. (b) Completely formatting the printer while the leading edge is in the first position, so that the printer has all necessary print commands to print a leading label in the roll, or series of labels in the roll. (c) Reversing the label leading edge by operating the drive roller so that the leading edge moves to an initial position for printing of the leading label in the roll by the print head. And (d) substantially immediately after step (c) initiating printing and advancing of the leading label, and cutting of the leading label from the roll, and continuing printing and advancing and cutting until the leading label or series of labels is or are printed and cut.
There is also preferably the further step of (e) at least during the practice of step (d) supplying a substantially uniform flow of pressurized gas between the second face of the label at the drive roller and the drive roller to prevent the pressure sensitive adhesive of the second face from sticking to the drive roller. Step (e) is typically practiced by supplying a substantially uniform flow of gas at a pressure of about 20-50 psi, preferably about 30 psi. Step (e) may be practiced substantially continuously through all of steps (a) through (d), or only when step (d) is being practiced. Step (d) is typically practiced with a delay of less than 0.5 seconds (typically less than 0.1 second) once reversing action pursuant to step (c) has been stopped.
As indicated above, the roll of linerless labels preferably comprises a thermal printable first face, and the print head comprises a thermal print head. In that case step (d) is practiced by applying heat to the first face of each label to effect printing while applying a compressive force by the print head to the first face of each label, e.g. a compressive force of about 9-10 pounds.
According to another aspect of the present invention a method of operating a printer to print linerless labels without the adhesive sticking to the drive roller is provided which comprises the following steps: (a) Operating the drive roller to advance the roll of linerless labels so that the second face is in contact with the drive roller and so that the leading edge of the linerless labels in the roll is aligned with the cutter, in a first position. (b) Formatting the printer. (c) Reversing the label leading edge by operating the drive roller so that the leading edge moves to an initial position for printing of the leading label in the roll by the print head. (d) Initiating and continuing printing and advancing of the leading label, and cutting of the leading label from the roll, until the leading label or series of labels is or are printed and cut. And (e) at least during the practice of step (d) supplying a substantially uniform flow of pressurized gas between the second face of the label at the drive roller and the drive roller to prevent the pressure sensitive adhesive of the second face from sticking to the drive roller. The details of steps (d) and (e) are as set forth above with respect to the first method described.
The invention also comprises a thermal printer for printing linerless labels in a roll. The thermal printer comprises the following elements: A support for take-off of linerless labels from a roll of linerless labels, the labels having a thermally printable first face, and a second face with pressure sensitive adhesive. A drive roller having a non-stick peripheral surface for engaging the second face to advance or reverse the labels. A thermal print head for engaging the first face of the labels and applying a compressive force on the labels biasing them into contact with the drive roller peripheral surface. A cutter for cutting labels from the roll after printing, the cutter on the opposite side of the thermal print head from the support. And an air knife disposed between the drive roller and the cutter for directing a substantially uniform flow of gas to the interface area between a label and the peripheral surface of the drive roller to prevent the adhesive of the second face of the labels of the roll from wrapping around the drive roller peripheral surface when the driver roller is rotated. The air knife typically comprises a gas-directing end having an end surface with at least three substantially evenly spaced gas-emanating openings formed therein. Each opening typically has a maximum dimension of about 0.01 to about 0.05 inches, preferably a diameter of about 0.03 inches.
It is a primary object of the present invention to effectively print linerless labels without the labels sticking to the printer drive roll, and particularly suited for thermal printers. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.